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notice of in the sacred record, seem to have been the appointed places where the profane rites of idolatry were celebrated, and which were, therefore, demolished by the express command of God. The same mode of worshipping the creature instead of the Creator, was practised among the ancient Persians and Babylonians.

their long captivity, which led them to that forgetfulness of God, which manifested itself at Mount Sinai, when they made the golden calf, and worshipped it.

In various regions of the world another species of idolatry has prevailed, which rests upon the same principles as that which has already been The principle of utility seems thus to have been noticed, although it involves a greater degree of the basis on which some of the earliest systems of complication in its details. When the selfish feelidolatry have been founded by mankind, when they ings of mankind, in a state of deplorable ignorance had lost the knowledge of the one true God; and in regard to the divine truths of religion, have led it is obvious, that it admits of an extensive de- them to pay homage to the great luminaries of the velopment and a varied application, in proportion heavens, the sun, the moon, and the stars,—to to the wants of the race, and to those inexhausti- the vegetable productions of the soil,—and to the ble sources, from which, through the continual inferior animals, because they perceived that they goodness of a merciful Creator, they may be sup- were dependent upon them for the continuance of plied. The consequence has been, that, in addi- life and all its comforts, it is not an improbable tion to the heavenly bodies, those creatures of supposition, that extending themselves in the same God which are useful to man have been exalted direction, towards objects of utility or advantage, as objects of worship by fallen beings, whose unthe idea would be entertained of exalting to superderstanding was no longer enlightened by direct natural honours, such of the human race as were emanation from the source of true religious know- eminently distinguished as the benefactors of their ledge, or through the medium of a revelation of country. Idolatry actually turned itself into this his holy will. None, however, of the material channel, and the knowledge of this fact affords an works of creation is calculated to make such a explanation of the mysteries of the pantheon. striking impression upon the senses and the mind The deification of the illustrious dead formed the of man, as the magnificent luminaries which adorn main foundation of the polytheism of the far celethe firmament; none to excite such a universal brated states of Greece and Rome, to which more feeling of the dependence of the race upon a higher particular allusion will afterwards be made. In power than their own for the continuance of life; the meantime, we may remark that this species of and none which seems so unceasingly to appeal idolatry is such a natural consequence of the operato mankind for the expression of thanks, on tion of the principle of false religion, that we find account of the obvious benefits which they confer. it established amongst the earliest nations of antiBut when the attention of the idolater was not quity, and prevailing in heathen lands, even to the fixed upon them,-when his mind was yet in a present day. The Egyptians paid homage not state of degrading ignorance in regard to the na-only to Osiris and Isis, the chief objects of idolature of the true God, and when, directed by the try, out to many other imaginary deities; the general principle of selfishness, it recognised utili- Persians also acknowledged a multiplicity of false ty alone as the foundation of homage, it was under gods. The objects of Hindu idolatry are endless, the necessity of seeking upon earth, for the objects presiding over the air, the sun, the moon, the to which it was to render its acknowledgments. rivers, and fountains. The following extract is Among the innumerable proofs of the Creator's from Davis's General Description of the Empire care, and of his kindness to the children of men, of China, and its Inhabitants :-" China has in we are struck with the abundant provision which fact her mythology in common with all other nahe has made for the support of life. The earth, tions; and under this head we must range the by culture, produces food for man; and the Al- persons styled Foh-shin-woong, Hoding-ty, and mighty hath replenished it with the inferior ani- their immediate successors who, like the demimals, which are given for his use, and contribute, gods and heroes of Grecian fable, rescued manin a very great degree, not only to the sustenta-kind, by their ability or enterprise, from the most tion, but to the comfort of his existence. Hence, another species of idolatry is that which made the vegetable productions of the earth, and the inferior tribes of living beings, the objects of worship. It is difficult to suppose, that the mind of man, in a state of civilization, should be capable of such degradation; but among the ancient Egyptians, although they were celebrated for their wisdom and learning, the productions of the field and garden were acknowledged as deities; and the mockeries of religious worship were offered to the ox, the dog, the cat, the crocodile. It seems exceedingly probable, that it was a portion of the idolatrous rites of the Egyptians, with which the mass of the Israelitish nation was leavened during

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primitive barbarism, and have since been invested with super-human attributes.”

One of the most natural consequences of raising the illustrious dead into objects of sinful homage and adoration, was image worship, which is another step in the downward progress of the human mind, when it is left to its own resources in the investigation of the great truths of religion. Nor was this practice confined to the construction and adoration of images of men; for representations were formed of the heavenly bodies, and of the inferior animals. But whatever may have been the objects which the image was intended to shadow forth, the degradation of worshipping the works of man's hands was equally

were given to bravery and manly fortitude, in the view of the approaching calamity. In such circumstances, Mr Stewart could not be indifferent to the interests of his country. He accepted, accordingly, of the appointment of chaplain to the Athole regiment of volunteers. This situation, which was without emolument, he the more readily undertook, hoping to be useful to the soldiers. His expectations, however, in this respect, were scarcely realized; and he felt himself exposed to many temptations which were far from agreeable to his high-toned Christian feelings.

great. The process is easily conceived, by which | from the pulpits of the parish churches, exhortations a transition may have been made from the original object of worship to its image, and especially, if a departed fellow-creature was that object. It is a pleasing gratification of affection to possess a likeness or representation of those who are respected and loved, after death has removed them from the observation of the eye; and the feelings from which it arises may have been the foundation of image worship in the minds of those who are already degraded by the practices of idolatry. The image itself being constructed, it was but one other act in advance, to assign to it the place which was occupied by its prototype. But in the progress of time, image worship, even without reference to a prototype, became prevalent over almost every part of the heathen world. Mankind having transferred their adoration to an object which their own hands had constructed, imagination lent its aid to complete what memory had begun, and the temples were filled with representations of beings, whose existence was merely potential.

The brief historical sketch which has now been given, will serve to illustrate the position, that human reason, unassisted, is incapable of arriving at the knowledge of the true God, or even of preserving it, when communicated, in a state of purity, unless when the mind is enlightened by personal revelation from heaven, or by the records of such revelation. Ignorance of God, therefore, along with moral depravity, affords a proof of the degradation and misery in which the posterity of

Adam have been involved since the fall. The deplorable consequences of such ignorance are most powerfully described by the Apostle Paul, in the account which he gives of the degraded condition of the heathens: "They changed the glory of the incorruptible God into an image made like to corruptible man, and to birds, and four-footed beasts, and creeping things. Wherefore God also gave them up to uncleanness, through the lusts of their own hearts, to dishonour their own bodies between themselves: who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever." Rom. i. 23-25. How wretched, then, and miserable is man, when left to himself,-born, living, and dying, in a state of alienation from God! How indispensable to his comfort and happiness is the glorious light of divine revelation!

BIOGRAPHICAL SKETCH OF THE

LATE REV. ALEXANDER STEWART, D. D.,
One of the Ministers of Canongate, Edinburgh.

(Concluded from p. 134.)

For some time, about the commencement of the present century, as is well known, the whole of Scotland was thrown into a state of alarm, by the dread of a threatened invasion from the French. Many of the people were trained to the use of arms; volunteer regiments were raised in different parts of the country, and even

At the invitation of several clerical friends in Ross

shire, he took a journey into that county in 1802, where he was welcomed by many of the pious ministers who had heard with joy of the revival at Moulin. A lively interest had been excited in his behalf; and wherever he went, his character and recent conversion had made him already extensively known. Among other esteemed brethren in that country, he visited Mr Charles Calder, minister of Urquhart, whose piety and devoted zeal Mr Stewart was now prepared fully to appreciate. He was persuaded to remain for a few days, and assist at the Sacrament, which was about to be dispensed; and he left the manse of Urquhart, gratefui to God for the refreshing intercourse he had there enjoyed. He was afterwards connected with the family by a closer tie, having married Mr Calder's eldest daughter; and on that occasion he says in a letter to Mr Black, "that it had pleased the Lord to enrich him with one of

the most precious temporal blessings he had to bestow."

As Mr Stewart's family was increasing, it was evi

dent that his income at Moulin was far from being ade

quate to their support. Arrangements were therefore attempted to be made to procure his translation to some

other parish. Several plans were at first in agitation these plans Mr Black of course entered warmly. But

to secure his valuable services for Edinburgh, and into

wall became vacant, and a very general desire was felt

before they were fully matured, the parish of Ding

in that town to secure the presentation for Mr Stewart.
For a time, however, the prospect appeared to be blast-

ed, when suddenly the whole aspect of affairs changed,
Stewart writes thus to Mr Black :-
and the appointment was obtained. On this subject Mr

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Prepare, my dear brother, to hear what will surprise you. Our times are in the Lord's hands, and his counsel shall stand. When every prospect and symptom of a change of place was removed, and when my people and I were set down again quietly and comfortably together, a new and unexpected turn has agitated the whole town-council of Dingwall, stating the ge

us afresh. The post brought me a letter subscribed by

neral desire of the parish to have me called to minister to them the word of life,-the providences that had frustrated the views of other candidates, and protaining a cordial and a pressing invitation to accept the moted those respecting my appointment, and concharge.

"Besides this, I had a letter from some of the serious inhabitants of the place, narrating the various turns of Providence, the offers made to other ministers connected with members of the council, their refusal, the persevering prayers, and other means employed by the godly all over the country, to gain the council; the delays, alarms, and disappointments, and at last the complete success of their wishes.

"You will learn every thing more particularly, when

I shew you the correspondence in Perth, if it please | God we meet there. When I considered all the steps and circumstances, a worldly engine put in motion by the breath of prayer, the iron-gate opening of its own accord,'-I could not but acknowledge the divine call, nor hesitate to accept it. I have, accordingly, written my answer, accepting the council's invitation. How to manage with the poor Moulin people, is the present difficulty. I took a number of them into my room last night, after worship, read my letters, and conversed with them. They were, indeed, sorely grieved, yet they did not deny the call being of God, and nothing but their personal attachment to me hindered them from fully acquiescing in it."

As the time drew near when he must leave his beloved flock at Moulin, Mr Stewart was delighted to see that their attachment to him continued unabated :"Now," says he, "that the time of my departure is almost at hand, you will be anxious to know how it fares with us all. There is really much composure and quiet acquiescence that prevail. Some weeks ago, I used only to make distant allusions to the situation in which we stood. Of late, I have thought proper to speak of our separation more explicitly, and make the mention of it somewhat familiar to our ears, so as to be able to think and talk of it without overpowering emotions. Our evening readings are crowded. The people seem to swallow the Word greedily, considering that their time may be short."

His reception in Dingwall was warm and cordial. Every one seemed to vie with his neighbour in shewing attention to their new pastor. They hung upon his lips as he faithfully and affectionately declared to them the words of eternal life; and in his private ministrations, he met with much to encourage him in the responsible charge which he had undertaken.

About seven months after he had entered upon his new charge, Mr Stewart was deeply affected by the mournful intelligence of the death of his warm friend and kind instructor, Mr Black, who was suddenly cut off on the 25th February 1806. The stroke was severe, more especially to one who regarded him as to a certain degree his spiritual father, by whom he had been begotten in the bonds of the Gospel. They had been united in the closest bonds of Christian affection, and the whole of their correspondence was pervaded by a spirit of tenderness and mutual charity, such as well becomes the consistent followers of the meek and the lowly Jesus. They, each of them, esteemed the other better than himself, and thus with the utmost cordiality, they aided and encouraged each other in the way to glory.

In little more than two years, however, Providence raised up to Mr Stewart, in place of the friend whom he had lost, one with whom he enjoyed a frequent and intiinate correspondence by letter, though they never met face to face. The first letter received from this hitherto unknown friend, who was a clergyman in Staffordshire, was dated in June 1808; and Mr Stewart acknowledges, in the letter which he wrote in reply, that he had been much comforted and refreshed by the unexpected communication.

In the discharge of his duties as a faithful minister of Christ, Mr Stewart was called to contend with many difficulties, which, had he not been a man of faith and prayer, might have discouraged and depressed him. The appearances were by no means so favourable at Dingwall as at Moulin, and accordingly we find him

thus describing the spiritual condition of his parish in a letter to a friend :

"To your queries about the state of religion in this parish, I fear I must answer in a complaining tone. Irreligion, indifference about spiritual concerns, attachment to the world, the intemperate use of spirituous liquors prevail to a melancholy extent. The doctrines of the Gospel are heard, in the main, I think, with indifference rather than dislike, which I ascribe to their not being understood or attended to. Some weeks ago, on occasion of preaching on the necessity of regeneration with close application, a strong and general dissatisfaction was openly expressed in many companies during the ensuing week, and some declared they were on the point of quitting the Church. I thought there was something hopeful in this movement. They seemed, at last, to have felt a little the sword's point. But, alas! it went no farther. They only knit their brows, muttered something against the preacher, and then sat as But still, amidst composedly on their seats as ever. this abounding aversion and resistance to the truth, the good seed appears not to have altogether perished. There are several, among the lower ranks, who shew an earnest desire for religious knowledge, and the company and fellowship of pious persons, and appear to receive the truth in the love of it.' Our advanced Christians bring me some encouraging intelligence of this While I am ready to cry, alkind, from time to time. most in despondency, 'Who hath believed our report?' one or two instances of awakened souls encourage me to say, 'Behold, is not here the arm of the Lord revealed!'

These remarks were intended to apply to the English congregation, who were by no means satisfied with his mode of preaching; while, by his Gaelic people, he was often strengthened and encouraged in his Master's work. By the blessing of God, however, upon his unwearied exertions, a decided change soon began to manifest itself in the outward aspect, at least, of the parishioners of Dingwall; and even where vital religion had not taken possession of the heart, there was an evident improvement in the external deportment of the people.

Zealous and active as Mr Stewart was in his ministerial duties, he found leisure to engage, to some extent, in literary pursuits. Besides occasional contributions to periodical works, he continued to prosecute his favourite study of the Gaelic language; and, as the fruit of his labours, he at length gave to the world his well-known Gaelic Grammar. So much were the public satisfied with the talent and research displayed in this work, that its author was requested, by the Highland Society of London, to revise the originals of Ossian's Poems, which they had resolved to publish. The task thus assigned him was one of no small difficulty, owing to the age and mutilated state of the manuscripts; he performed it, however, with singular ability and success. Such was the reputation which Mr Stewart had now acquired as a Gaelic scholar, that a proposal was made to him by the Highland Society of Scotland to execute a Dictionary of the language: at the same time an offer was held out of a handsome remuneration on the completion of the work. After weighing the matter fully, he declined the proposal, chiefly on the ground that it would withdraw his mind too much from the laborious duties of his spiritual calling. At the same time he devoted his leisure hours to the translation of the Shorter Catechism into Gaelic, the revisal of the Gaelic Psalms, and the preparation of some valuable Tracts in the same language. Dr Stuart of Luss also applied to

him for assistance in the great work which had been | days' illness. This last stage of his journey was indeed committed to his hands-a revision of the entire Gaelic Bible.

While thus adverting to Mr Stewart's useful labours as a translator, an incident may be mentioned in connection with this subject, which displays, in a very striking light, his amiable dispositions. Having observed in the reports of the Baptist Missions a letter from the celebrated Dr Carey of Serampore to Mr Fuller, complaining of the weak state of his eyes, and begging Mr Fuller to procure for him a copy of Van Der Hooght's edition of the Hebrew Bible, Mr Stewart immediately said to himself, "I wish the worthy man had my copy," and sitting down, wrote, offering it, and requesting to be informed how it might be transmitted. The offer was gladly accepted, and "I with great pleasure," he says, "followed the direction, wrote a letter of some length to Carey, and sent off my parcel to London. I dare say you remember my favourite Hebrew Bible in two volumes. I parted with it, with something of the same feelings that a pious parent might do with a favourite son, going on a mission to the heathen,-with a little regret, but with much good will." This circumstance led to an interesting correspondence with Mr Fuller and Dr Carey, which was carried on for some time.

Mr Stewart's labours, both as a faithful minister and an ardent lover of literature, were so multiplied and exhausting, that his health was at length seriously affected; and in two years after his settlement at Dingwall he was seized with a severe and protracted illness, which weakened his constitution. In 1811, four years after his previous attack, symptoms of an internal disorder began to manifest themselves, which, though it might be alleviated for a time, must sooner or later, bring him to the grave. He still continued, however, amid frequent paroxysms of the most acute pain, to discharge his duties in his parish. But the following extract from a letter which he wrote to a friend, shews that he sometimes gave way to feelings of despondency, the consequence, probably, of his bodily ailments:

"I wish I could cheer you with good news from this little town and parish, but, alas! we seem to be doing nothing, almost quite dead. I was laid aside for some weeks, having been seized with a topical complaint, which might have proved fatal, no surgeon being at hand, if I had not been mercifully directed and enabled to use the proper means for procuring relief. I hoped that my own spirit had been softened and warned by this visitation, but, alas! all was like the morning cloud. My own vineyard I have not kept, and now it is growing over with thorns. I have not a heart nor a soul to employ in the honourable service of the most honourable of all Masters, but I am to try, at least, to employ my silly body in the work, and am to begin this day a course of parochial examination.

Woes me! for the day goeth away, the shadows of the evening are stretched out over me, and little or nothing done for Him that loved me, and gave himself for me,-unprofitable servant! !"

In addition to his personal sufferings, Mr Stewart was called to endure a heavy trial in the death of his beloved father-in-law, Mr Calder of Urquhart. The loss of such a man was deeply felt, not merely in his own parish, but in the whole surrounding neighbourhood. His death is thus described, briefly, by Mr Stewart: "He was removed to glory," says he, "after seven

a very painful one to the flesh, but he was blessed with perfect composure of mind. While he shewed the deepest self-abasement, yet the love, the grace, the fulness, and glory of his adorable Redeemer, were his constant theme. Though torn with acute inward pain, he never uttered a complaining word; not a feature of his face indicated a struggle to suppress complaint. The most serene, resplendent luminary of our horizon, is set. His affectionate, bereaved parish, are left for a time as sheep without a shepherd. His pious, venerable widow, bowed down with infirmities and broken tender attached daughters, who doated on their father health, is left a solitary pilgrim in the wilderness. His with almost more than filial piety, have felt a pang in parting with him, which time alone can heal."

For some years Mr Stewart continued to officiate regularly every Sabbath, and to discharge his parcchial duties with fidelity, though amid much weakness. At length, in 1819, the symptoms of his disorder had become so alarming, that he was strongly advised to set out for Edinburgh, that he might obtain the most skilful medical aid. The journey he accomplished without any material injury to his health, but having experienced no permanent relief from the means employed, he returned home. As the disease still increased in severity, however, it was thought to be of great importance that he should again venture on a journey southward, and try the effects of a winter's residence in Edinburgh.

He had not been more than a few months in the me

tropolis, when the death of the minister of the first charge of Canongate led to his appointment to that charge, where, in conjunction with his truly excellent colleague, Dr Buchanan, he laboured during the short remaining period of his life. The disease, from which he had suffered so much, soon returned with unabated severity, and in the course of 1820 he was several months laid aside from duty. His constitution, already much enfeebled, sustained a violent shock from this attack, and though, after a partial recovery, he resumed his pulpit duties for a time, the Sacramental Sabbath, in May 1821, was the last occasion on which he had strength sufficient to appear in public. From that day he gradually became weaker in body, and more sensibly impressed with the prospect of his approaching departure.

to rest, My dear boys,' said he, take your father's "Two of his sons having laid him down one evening blessing, it may be the last time I will give it you.and make his countenance to shine upon you, and give May the God of your fathers bless you, and keep you, you peace!'

"On another occasion, to one of them, supporting him under a fit of pain, he said, 'You will not have it to do long.' All shall be well with you, my dear father,' said the affectionate youth. O yes,' cried he immediately, I have evidences which I cannot deny, that the Lord has been gracious to me. But I now live by faith, I have no sensible enjoyments.'

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"On these occasions of intense pain, the grace of patience had its work so perfect, that it was a common remark of his, David had to sing of mercy and judgment together, but it is all mercy with me.'

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Death, at length, came as a release from his sufferings, and on Sabbath the 27th of May his happy spirit winged its flight to another and a better world. To him to live" had been "Christ," and, of course, "to die was" unspeakable "gain." "He had finished his course, he had kept the faith," and it was now his high privilege to receive that “crown of glory which

"Blessed had been laid up for him in the heavens." are the dead that die in the Lord from henceforth; yea, saith the Spirit, that they may rest from their labours; and their works do follow them."

CHRISTIAN PHILOSOPHY.

No. VIII.

MECHANICS.

BY THE REV. JAMES BRODIE,

Minister of Monimail.

MECHANICS may be aptly defined the science of motion, as practically applied by man; for the immediate object of all our contrivances is either to produce, or to regulate motion. Machines are divided into two classes, according to the kind of motion on which their action depends, each class being regulated by its own peculiar laws.

UNIFORM MOTION.-When the motion is uniform, we have only to attend to three particulars the force employed, the quantity of matter moved, and the velocity communicated. These bear to each other certain definite relations, which may be expressed in the following propositions, naturally deducible from the laws of motion, formerly described :

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I. The force, being directly proportioned both to the quantity of matter and to the velocity, is always equivalent to the product of the two. If, for example, a body weighing twenty pounds, moves at the rate of two miles in a minute, the multiplication of twenty by two will give the measure of the force necessary for producing or checking its speed.

The wheel, or, as it is sometimes termed, the wheel and axle, may be considered as merely a succession of levers. The centre or axis is the fulcrum; one of the forces is applied to the circumference of the wheel, and the other to the circumference of the axle. Their respective velocities being proportioned to the circles they describe, they are inversely to each other as their distances from the centre of motion. If a power, for example, of one pound be applied to the circumference of a wheel eight feet in diameter, it will be an exact counterpoise to a weight of eight pounds, on an axle whose diameter is one foot. Wheels may be combined together, and when the axle of the one machine is so connected with the wheel of the other, (by means of teeth or bands) that their circumferences move with equal rapidity, the mechanical advantage is in the compound ratio of the simple machines employed.

The wheel, either by itself, or combined with other mechanic powers, is employed in cranes, capstans, and similar contrivances, for raising heavy weights. It is also employed in watches and clocks, in corn and spinning mills, and in the greater number of large and complicated machines.

The third mechanical power is the pulley, which is a small wheel turning upon an axis, and having a groove The fulcrum is in its circumference to admit a rope. at one end of the rope, the power at the other, and the weight is supported by the axis of the pulley. As in the lever and wheel, the weight and power are inversely to each other as their distances from the fulcrum or centre of motion. The advantage gained by a single pulley is as two to one.

machines which are intended to be frequently moved; their most common application is to the rigging of ships.

Pulleys may be combined together in various ways and with various effects. They are very light, and ocII. Two bodies differing in size, and moving in op-cupy little room, and are therefore employed in those posite directions, will balance each other when their velocities are inversely proportioned to their weight, or, in other words, when the weight of the one body, multiplied by the space through which it passes, is equal to the weight of the other, multiplied by the space which it goes over. In all mechanical calculations, it is considered that we have a certain quantity of matter to be put in motion, which we denominate the weight, and mark W, and a given velocity to be communicated to it; while, in order to accomplish this end, we have another body, which is termed the power, and marked P, acting in a different direction, and to which any requisite motion can be applied.

All the varied contrivances, exhibiting uniform motion, consist of some combinations of six simple machines, the lever, the wheel, the pulley, the inclined plane, the wedge, and the screw. These are commonly called the mechanic powers, or elements of machinery. The lever is an inflexible bar, resting on a fulcrum In the first or prop, on which it turns as a centre. kind of lever, the weight and power are attached on opposite sides of the fulerum. Of this the balance affords one of the most familiar illustrations. In the second variety, the weight and power are on the same side of the fulcrum, the lever resting on one end. Of this the druggist's knife, fastened at one end, affords an example, as does the wheelbarrow, in which the axle is the fulcrum. In all varieties of the lever, the spaces passed over by the weight and power are proportioned to their distance from the fulcrum: in order, therefore, to produce an equilibrium, the lighter either of them is, the greater its distance must be.

Levers are commonly employed in raising great weights to small distances, as in the crow-bar and handspoke; they are also employed in some cutting instruments, such as scissors and pincers, and are frequently combined with other machines, and sometimes with each other. The moveable bones of animals are all levers, and exhibit very beautiful illustrations of the principles we have now been describing.

The inclined plane, as its name imports, is a sloping surface along which the weight is moved. Without a reference to figures, it is hardly possible to give an intelligible explanation of its properties, which vary aecording to the direction in which the power acts; but it holds universally true, that the smaller the elevation of the plane, the less is the resistance offered by the weight.

It is occasionally introduced, in combination with other contrivances, into complicated machines, but is most commonly employed when very great weights are to be moved, as in making excavations, and in raising large blocks of stone for building. All acclivities, whether natural or artificial, up which any body is rolled or drawn, must be considered as inclined planes.

The wedge, when applied to uniform motion, is merely a variety of the inclined plane. The thinner the back or head of the wedge, and the greater the length, the greater will be its power. It is commonly employed in splitting wood and stone, and in raising weights to a small height. A great variety of cutting instruments, such as chisels and knives, which act by simple pressure, are also to be considered varieties of this mechanic power. When the power acts by percussion, as in the hatchet, or where pressure is combined with a sliding movement, as in the knife, the effect depends partly on the mechanical advantage gained by the wedge, and partly on principles, to be afterwards explained, when we come to treat of accelerated motion.

The form of the screw is familiar to all. It may be considered an inclined plane, wound round a cylinder. As the weight is raised at every turn, a height equal to the distance between the threads or spirals of the screw, the power will bear the same proportion to the weight, that this distance does to the circle described by the power. The screw is seldom employed without being combined with the lever, which greatly increases the effect of the machine, by enlarging the space passed

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